A coolant cooler dissipates excess heat produced by an internal combustion engine of a motor vehicle to ambient air. Moreover, with supercharged internal combustion engines, a charge-air cooler cools air, which has been heated and compressed in a supercharger, and dissipates heat to ambient air. The operations of cooling charge air and coolant are fundamentally different. The coolant undergoes only a small drop in temperature because the coolant has a high heat capacity. A large heat quantity thus can be exchanged even with slight cooling. In contrast, the charge air temperature is considerably higher when it enters the charge-air cooler and has to be considerably lower than that of the coolant as the charge air exits.
Charge-air coolers can be air cooled or liquid cooled. In liquid-cooled charge-air coolers, more straightforward charge-air guidance is usually possible, and the overall volume of these charge-air coolers can be smaller than the air-cooled design. If the engine coolant cools the charge air, the charge air can only be cooled approximately to the coolant temperature. If a lower charge-air temperature is sought, it can only be achieved by an additional coolant circuit that is capable of producing a lower outlet temperature or, more straightforwardly, by air-cooled charge-air coolers. The air-cooled design is widely used in passenger cars and commercial vehicles. The charge-air coolers are thus generally air-cooled charge-air coolers.
It is known from the publication ATZ Automobiltechnische Zeitschrift (Automotive Journal) (1981), No. 9, pages 449, 450, 453, to arrange the charge-air coolers upstream of the coolant cooler and have part of the end surface of the coolant cooler overlap the charge-air cooler on the air side. The reason for this arrangement is that, in the case of the charge-air cooler, a lower target temperature has to be reached than in the case of the coolant cooler. The lower target temperature is ensured by cooling with fresh air flowing against the same. This conventional arrangement is disadvantageous in that cooling air flowing on the air side becomes heated to a very pronounced extent in the upstream charge-air cooler. Because the heated air reaches the downstream coolant cooler, it can only slightly cool the coolant in the overlapping coolant-cooler part. The coolant cooler of such an arrangement thus requires a relatively large surface area to achieve the necessary cooling capacity. Moreover, very large cooling-air streams are necessary, and they require in some cases very high fan capacities.
European Patent Application EP 522 288 discloses a heat exchanger arrangement that has a coolant cooler and a charge-air cooler. The charge-air cooler is of split design and, in relation to a cooling air stream, has one charge-air-cooler part located upstream of the coolant cooler and one charge-air-cooler part located downstream thereof. This arrangement makes it possible for at least one part-surface of both of the charge-air cooler and of the coolant cooler to be exposed to fresh air. Such an arrangement has a disadvantage in that, on account of the charge-air cooler being split into two charge-air-cooler parts, increased design outlay is necessary, in particular in terms of the charge-air-side connection of the two charge-air-cooler parts to one another for passing on the charger from one charge-air-cooler part to the other. Because this operation involves the charge air being passed on, there is an additional pressure drop in the charge air. Furthermore, there is an increase in the installation space, in particular the installation depth in the air-flow direction within the motor vehicle in comparison with a conventional arrangement, since three heat-exchanger planes, namely the first part of the charge-air cooler, the coolant cooler, and the second part of the charge-air cooler, are arranged one behind the other on the air side.
European Patent Application EP 522 471 discloses a heat exchanger arrangement that has a coolant cooler and a charge-air cooler. Both the coolant cooler and the charge-air cooler are of split design. This arrangement likewise is disadvantageous in that increased design outlay is necessary for passing on the charge air and the coolant to the respectively associated charge-air-cooler part and coolant-cooler part.